1. Field of the Invention
The present invention relates to a positive resist composition for use in the production of semiconductors, e.g., IC's, in the production of circuit boards for liquid crystals, thermal heads, etc., and in other photofabrication processes. More particularly, the invention relates to a positive resist composition suitable for use in applications where resists are exposed to a light having a wavelength of 250 nm or shorter, such as far ultraviolet rays, or irradiated with electron beams or the like.
2. Description of the Related Art
A chemical amplification type positive resist composition is a pattern-forming material which, upon irradiation with radiation, e.g., far ultraviolet rays, generates an acid in the exposed areas and comes to have a difference in solubility in a developer between the actinic-ray-irradiated areas and the unirradiated areas based on a reaction catalyzed by the acid. A pattern is thus formed on a substrate.
In ArF resist processing, formation of contact holes of 120 nm or smaller is desired. However, the degree of completion of ArF resists is lower than those of resists heretofore in use, such as i-line resists and resists for KrF excimer lasers. It is thought that the formation of a hole pattern of 120 nm or finer is difficult even with an ArF excimer laser illuminator having an NA of 0.90, which may come to be produced in the future.
Resist compositions which comprise a hydroxystyrene. resin and are intended to be used for obtaining a pattern having a desired hole size only through a flow bake process are disclosed in, e.g., JP-A-2002-196497. However, the hydroxystyrene resin transmits almost no ArF excimer laser light and, hence, these resist compositions have not been usable as an ArF resist at all. Resist compositions for ArF exposure which contain alicyclic structures are disclosed in, e.g., JP-A-2000-159758, JP-A-2000-330287, JP-A-2000-338674 and JP-A-2002-161116. However, since this resin has a glass transition temperature as high as 150° C. or higher due to the alicyclic structures contained therein, the resist pattern does not thermally flow upon heating at a practical flow temperature (200° C. or lower).
Furthermore, a resist composition containing a blend of acid-decomposable resins the relationship between which concerning glass transition temperature is reversed through exposure and resultant decomposition is disclosed in JP-A-2002-229210. However, all the resins shown therein as examples contain styrene structures and hence have an exceedingly low transmittance of ArF excimer laser light. Consequently, necessary resolution has not been obtained with the resist composition in contact hole formation through exposure with an ArF excimer laser.